The role of the pituitary in regulating various aspects of sexual maturation and fertility has become very important. Various physiological substances have been isolated which affect the synthesis and secretion of gonadotropin, but recently a non-steroid substance has been isolated which inhibits the specific secretion of FSH by the pituitary. It has been reported that this substance is produced in the male by specific cells, Sertoli cells. The goal of this research is fivefold. First, since Sertoli cells produce "inhibin", an attempt will be made to radiolabel the secreted inhibin secreted in vitro by Sertoli cells maintained in defined media. Second, various modern isolation techniques such as high pressure liquid chromatography, hydrophobic chromatography and dye matrix separation will be used for various steps of purification of "inhibin". Third, to investigate the chemical nature of inhibin using various protein and carbohydrate sequencing techniques. Fourth, the structure of the "inhibin" produced in vitro by Sertoli cells will be compared to the in vivo product as well as to various testicular and follicular extracts. Fifth, to investigate the mechanism(s) of action of various stimulators and inhibitors on the synthesis and secretion of Sertoli cell inhibin (i.e., tunicamycin, puromycin, gonad steroids, and gonadotropin hormones). The major objective of this study is to better understand the chemical nature of inhibin and its mechanism of synthesis and secretion in a model (rat) system in order to understand regulation of fertilty in the human.